1. Field of the Invention
This invention relates to an outboard motor steering control system, particularly to an outboard motor steering control system for controlling steering of multiple outboard motors.
2. Description of the Related Art
Conventionally, boats are commonly equipped with two or more outboard motors mounted side-by-side in what is called a “multiple outboard motor installation,” as disclosed, for example, in Japanese Laid-Open Patent Application No. 2004-52697 (particularly paragraphs 0014 to 0016, FIG. 1). In addition, outboard motor steering control systems are proposed in recent years in which actuators are installed to operate the multiple outboard motors separately or individually.
In the case of multiple outboard motor installation, the straight course-holding performance or turning performance of boat can be improved by giving the outboard motors different steering angles in response to the cruising conditions so as to regulate their relative angles. To be more specific, straight course-holding performance can be improved by establishing the relative angles so that extensions of the propeller shafts intersect forward of the outboard motors in the direction of forward travel, thereby enabling to restrain the lateral fluctuation of the boat.
Turning performance also can be improved by making the extensions of the propeller shafts intersect rearward of the outboard motors in the direction of forward travel, when an absolute value of rotation angle of the steering wheel equal to or greater than a predetermined value, i.e., when the boat is controlled to make a relatively great turn. In other cruising conditions, for instance, when an absolute value of rotational angle of the steering wheel is less than a predetermined value (i.e., when the boat is controlled to make a relatively small turn), the outboard motors are steered synchronously by making the extensions of the propeller shafts parallel to each other, in other words, setting their relative angles to zero.
When actuators are installed to operate multiple outboard motors separately or individually, however, it is difficult to make control to steer the outboard motors synchronously to achieve desired relative angles therebetween, resulting in insufficient steering performance.